As used herein, the term “smoking article” includes smokeable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes and also heat-not-burn products.
The non-porous tipping paper of a conventional filter cigarette often includes ventilation holes at a location which overlaps the filter. The holes allow air to be drawn into the filter during smoking to dilute the smoke exiting the mouth end of the smoking article. The holes are of relatively large diameter and are generally formed by perforating the tipping paper and the plugwrap paper by passing the filter under a pulsing laser beam. Another option is to use a pre-perforated tipping paper coupled with a porous plugwrap paper. An example of a pre-perforated tipping paper and a porous plugwrap paper is shown in FIGS. 1 and 2.
Generally a filter cigarette also includes a substantially homogeneous and porous cigarette paper, which bounds a rod of smokeable material such as tobacco. The porous nature of the cigarette paper allows a degree of gaseous exchange between the smokeable material and the exterior of the paper. However, the volume of gaseous exchange through the cigarette paper significantly reduces as the length of the rod of smokeable material, and therefore the surface area of the cigarette paper, reduces during smoking. There is therefore significant puff-by-puff variation in the dilution of the smoke entering the filter from the rod of smokeable material. Dilution can reduce significantly from the first puff to the last.